requestConfig := &msgraph_drives.ItemItemsDriveItemItemRequestBuilderGetRequestConfiguration{
	QueryParameters: &msgraph_drives.ItemItemsDriveItemItemRequestBuilderGetQueryParameters{
		Select: ["size"], // anything else, but this was my main issue
	},
}

driveItemIds := []string{} // just add a driveItemId for any non-empty file in OneDrive/Sharepoint
driveItemIdToStepId := make(map[string]*string, len(driveItemIds))

for _, driveItemId := range driveItemIds {
	reqInfo, err := client.Drives().ByDriveId(driveID).Items().ByDriveItemId(driveItemId).ToGetRequestInformation(ctx, requestConfig)
	if err != nil {
		panic(err)
	}

	step, err := batchCollection.AddBatchRequestStep(*reqInfo)
	if err != nil {
		panic(err)
	}

	driveItemIdToStepId[driveItemId] = step.GetId()
}

batchResponse, err := batchCollection.Send(ctx, client.GetAdapter())
if err != nil {
	panic(err)
}

for _, driveItemId := range driveItemIds {
    stepID := driveItemIdToStepId[driveItemId]
    driveItem, err := msgraphcore.GetBatchResponseById[models.DriveItemable](
        batchResponse, *stepID, models.CreateDriveItemFromDiscriminatorValue,
    )
    if err != nil {
        panic(err)
    }

    if driveItem.GetSize() == nil {
        panic(fmt.Errorf("size is nil for driveItem %s", driveItemId))
    }
}